Magnification
L5
Using units
1 km
1000 m
1m
100 cm
1 cm
10 mm
1 mm
1000 µm
1 µm
1000 nm
• Microscopes are useful
because they magnify things,
making them look bigger.
• There is a minimum distance
between two objects when
you can see them clearly as
two separate things.
• If they are closer together
than this, they appear as one
object.
Resolution is the ability to distinguish between two different points that
are very close together
x40
x100
Resolving power
• Light microscopes can magnify around 2000
times
• They have a resolving power of about 200nm
(however standard school ones only go up to
about x400)
• Electron microscopes can magnify objects up
to 2 million times
• They can have a resolving power of between
10nm and 0.2nm
The electron microscope
• Electron microscopes use a beam
of electrons instead of beams or
rays of light.
• They are much larger and much
more expensive
• They can achieve much greater
resolution than a light microscope
• Living cells cannot be observed
using an electron microscope
because samples are placed in a
vacuum.
• the scanning electron microscope
(SEM) has a large depth of field so
can be used to examine the surface
structure of specimens
• the transmission electron
microscope (TEM) is used to examine
thin slices or sections of cells
or tissues
• Transmission Electron Microscopes (TEMs) have a maximum
magnification of around ×1,000,000
• The resolution is now less than 1 nm.
• Electron microscopes revealed structures in cells that are not visible
with the light microscope.
• Scanning Electron Microscopes have a magnification of up to
×30,000).
• The resolution of a SEM is approximately 50 nm.
Calculating the size of an object
• As long as you know or can measure two factors then you can work
out the size of the third
Image size
Actual size = Magnification
Actual size =
20mm
100
= 0.2 mm = 200µm
Multiply by 1000 to
work out in µm